This article is one in a series offering tips on boating skills and seamanship prepared for The Citizen by the U.S. Coast Guard Auxiliary.
Nautical charts are to a boater what maps are to a driver. A chart is used to aid in navigation. It is a representation of a portion of the earth's surface showing information useful to boaters.
Today's charts are available not only on paper, but on CDs and DVDs. Electronic charts, indeed electronic navigation, is growing in popularity.
Usually charts are drawn “to scale,” which means that the sizes of objects in the drawings are proportional to their actual sizes. A chart may show both water and land areas.
The National Ocean Service (NOS) of the National Oceanic and Atmospheric Administration (NOAA) publishes charts of all U. S. waters. You can buy them from NOS or from any of the local marinas and marine supply stores.
The information contained on a single chart is staggering! It would take several books to include what is on a single chart. Among the items one finds on a chart are aids to navigation and their meaning (discussed in an earlier column), water depths, types of bottoms (S-sand; M-muddy; St-stones; G-gravel; information helpful in a number of ways including anchoring). In addition the chart includes the compass rose with its variation figure, distance scales, latitude and longitude figures, clearance under bridges, location of locks, etc.
One of the primary functions of charts is to help the mariner plot a course to its intended destination, avoiding dangerous areas. Navigation involves getting from where you are to where you want to be. To do this, you must be able to determine your present position and the position to which you wish to go.
It is easy to read your latitude and longitude on the chart, thus determining your exact position. Distance to the destination is equally easy to calculate. In turn, that will determine the amount of time and fuel needed to reach the destination.
As stated earlier, electronic charts assisted by GPS could do some of these calculations faster. The prudent mariner knows how to do both in the event of a power failure or some other emergency which renders the electronics inoperable. A chart will show dangers to avoid on the way to your destination. A GPS may not!
Usually, charts are used in conjunction with a marine compass. A good compass, which contains an oily or alcohol-based liquid, is built to withstand the vibrations and pounding of boats moving at high speeds or through rough waters. The compass of a sailboat must be able to operate satisfactorily when the boat heels over at an angle.
Mariners know how vital a compass can be in navigation. It tells you the course to steer to get to your destination and helps you to determine your position along the course.
Boaters know that the compass responds to magnetic north rather than the true north. The charts grid is oriented to true north. The difference in angle is called variation and most charts show variation (the figure to adjust for the difference) in the compass rose. A further adjustment is made for deviation. The magnetic compass is influenced by magnetic fields near it such as radio, GPS, other metallic objects and has to be adjusted accordingly.
Protect your compass from excessive heat and direct sunlight. If a compass leaks fluid from a ruptured seal, it becomes unusable. It is a good idea to have a light to read the compass at night, although a number of good compasses are equipped with an internal red light.
You can learn more about charts and compasses and acquire navigation skills by attending the safe boating courses offered free of charge by the U.S. Power Squadron and the U. S. Coast Guard Auxiliary. For information on the next available course, call the Ithaca Flotilla at (607) 273-7175 or your local Power Squadron.
John E. Keshishoglou is the
commander of the Ithaca Flotilla 22
Today's charts are available not only on paper, but on CDs and DVDs. Electronic charts, indeed electronic navigation, is growing in popularity.
Usually charts are drawn “to scale,” which means that the sizes of objects in the drawings are proportional to their actual sizes. A chart may show both water and land areas.
The National Ocean Service (NOS) of the National Oceanic and Atmospheric Administration (NOAA) publishes charts of all U. S. waters. You can buy them from NOS or from any of the local marinas and marine supply stores.
The information contained on a single chart is staggering! It would take several books to include what is on a single chart. Among the items one finds on a chart are aids to navigation and their meaning (discussed in an earlier column), water depths, types of bottoms (S-sand; M-muddy; St-stones; G-gravel; information helpful in a number of ways including anchoring). In addition the chart includes the compass rose with its variation figure, distance scales, latitude and longitude figures, clearance under bridges, location of locks, etc.
One of the primary functions of charts is to help the mariner plot a course to its intended destination, avoiding dangerous areas. Navigation involves getting from where you are to where you want to be. To do this, you must be able to determine your present position and the position to which you wish to go.
It is easy to read your latitude and longitude on the chart, thus determining your exact position. Distance to the destination is equally easy to calculate. In turn, that will determine the amount of time and fuel needed to reach the destination.
As stated earlier, electronic charts assisted by GPS could do some of these calculations faster. The prudent mariner knows how to do both in the event of a power failure or some other emergency which renders the electronics inoperable. A chart will show dangers to avoid on the way to your destination. A GPS may not!
Usually, charts are used in conjunction with a marine compass. A good compass, which contains an oily or alcohol-based liquid, is built to withstand the vibrations and pounding of boats moving at high speeds or through rough waters. The compass of a sailboat must be able to operate satisfactorily when the boat heels over at an angle.
Mariners know how vital a compass can be in navigation. It tells you the course to steer to get to your destination and helps you to determine your position along the course.
Boaters know that the compass responds to magnetic north rather than the true north. The charts grid is oriented to true north. The difference in angle is called variation and most charts show variation (the figure to adjust for the difference) in the compass rose. A further adjustment is made for deviation. The magnetic compass is influenced by magnetic fields near it such as radio, GPS, other metallic objects and has to be adjusted accordingly.
Protect your compass from excessive heat and direct sunlight. If a compass leaks fluid from a ruptured seal, it becomes unusable. It is a good idea to have a light to read the compass at night, although a number of good compasses are equipped with an internal red light.
You can learn more about charts and compasses and acquire navigation skills by attending the safe boating courses offered free of charge by the U.S. Power Squadron and the U. S. Coast Guard Auxiliary. For information on the next available course, call the Ithaca Flotilla at (607) 273-7175 or your local Power Squadron.
John E. Keshishoglou is the
commander of the Ithaca Flotilla 22
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